NZ First will cast his proxy vote along National Party lines, instead of its own. Ms Martin told RadioLIVE on Wednesday night they had "nothing really" to gain from the arrangement.

"We believe the people of Botany deserve the representation that they voted for. They voted for a National Party MP and so we're prepared to take their representation and use it on their behalf while this thing gets sorted out, basically."

National campaigned vociferously against the Electoral (Integrity) Amendment Bill - popularly known as the waka-jumping law - which would give them the right to boot Mr Ross from Parliament completely if his actions "distort" the proportionality of Parliament. Voting with the National Party would weaken that argument. National hasn't ruled out trying to expel Mr Ross.

"It's an option for them. They railed against it, but it's an option for them," said Ms Martin.

"It would be really interesting if they found themselves needing to use it. What I think they're probably finding… is everything they said about it is probably not true. It's not that easy to get rid of an elected MP."

While NZ First is happy to cast his vote for him, Ms Martin says Mr Ross should seriously consider resigning his seat.

"He has broken away from the party he campaigned with. He was elected on their platform. The people of Botany elected him on that platform. We think that he should go, and go back into a by-election, just the same way Winston Peters did. But we can't force him to do that."

When National moved to expel Mr Peters from the party in the early 1990s, he instead resigned and triggered a by-election - which he won easily as an independent, and went on to form New Zealand First.

Ms Martin says she's not sure why Mr Ross hasn't resigned, as he originally promised. Asked if it was to keep the hefty salary, she said she "couldn't speculate".

"I have no idea what Jami-Lee Ross' financial circumstances are. He could be rich as houses, for all I know."

And she's not sure what Mr Ross, who has released embarrassing secret recordings of himself and senior National Party figures, plans to do next or what his endgame might be.

"I don't know. I've never seen anything like this in my life. To be frank, I have no idea what is going on over there. Obviously it's terribly, terribly sad that a young man… has found himself unwell."